1. Field of Endeavor
The present disclosure relates to parameter estimation, and more particularly to a parameter estimating apparatus for permanent magnet synchronous motor driving system.
2. Background
This section provides background information related to the present disclosure which is not necessarily prior art.
Permanent magnet synchronous machines (PMSMs) driven by voltage inverters are generally operated under a speed control mode or a torque control mode. The PMSMs used for the speed control mode may include such industrial fields as hoist fields including elevators and cranes, and variable speed operation fields including fans and pumps. The PMSMs used for the torque control mode may include such industrial fields as traction motors for electric vehicles.
A difference may occur between a torque outputted by an inverter and an actually outputted torque, because a magnetic flux is saturated according to load situation in the PMSM. Now, a driving system of a PMSM according to prior art will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram illustrating a PMSM according to prior art, where a PMSM driving system is illustrated that is driven by an inverter in which a vector control independently controlling a magnetic flux current and a torque current is realized.
Referring to FIG. 1, the PMSM driving system according to prior art includes an inverter (100), a PMSM (200) and a rotor position detector (210). The inverter (100) receives a reference torque to output voltages for driving the PMSM (200) in response to the reference torque.
The rotor of the PMSM (200) is attached with the rotor position detector (210) to calculate or measure rotor position and rotor velocity. The rotor position and rotor velocity calculated or measured by the rotor position detector (210) is used for coordination conversion by coordinate converters (130, 170). A current command generator (110) outputs a current command of synchronous reference frame. A current controller (120) serving to control the current command, outputs d/q axis voltage of the synchronous reference frame.
A coordinate converter (130) uses the rotor position information received from the rotor position detector (210) to convert an output voltage of the current controller (120) to a voltage of a stationary reference frame. An over-modulator (140) functions to convert the output voltage of the coordinate converter (130) to a voltage that can be combined by an inverter unit (150).
The inverter unit (150) is a voltage type inverter including a power semiconductor, and applies command torque-tracing voltages to the PMSM (200).
Current sensors (161 to 163) measure a phase current between the PMSM (200) and the inverter unit (150), and the current measured by the current sensors (161 to 163) is coordinate-converted by the coordinate converter (170) and fedback to the current controller (120).
Now, the PMSM system of FIG. 1 will be described.
A torque of the PMSM (200) may be obtained by the following Equation 1:
                              T          e                =                                            3              2                        ⁢                          P              2                        ⁢                          λ              ds              r                        ⁢                          i              qs              r                                -                                    λ              qs              r                        ⁢                          i              ds              r                                                          [                  Equation          ⁢                                          ⁢          1                ]            where, an superscript ‘r’ represents a parameter of a synchronous reference frame, and a subscript ‘s’ is a parameter of stationary reference frame, P represents the number of poles of a motor, λdsr, λqsr are rotor magnetic fluxes of d/q axis synchronous reference frame on the stationary reference frame, and idsr, iqsr are currents of d/q axis stationary reference frame on the synchronous reference frame, where magnetic flux of rotor on d/q axis the synchronous reference frame may be defined by the following Equations:λdsr=Ldsidsr+λf  [Equation 2]λqsr=Lqsiqsr  [Equation 3]where, Lds and Lqs respectively represent d/q axis inductance on synchronous reference frame, λf represents a magnet flux linkage by a permanent magnet.
If Equations 2 and 3 are plugged into Equation 1, a torque of the PMSM (200) may be expressed by the following Equation 4:
                              T          e                =                              3            2                    ⁢                                    P              2                        ⁡                          [                                                                    (                                                                                            L                          ds                                                -                                            ⁢                                              L                        qs                                                              )                                    ⁢                                      i                    ds                    r                                                  +                                  λ                  f                                            ]                                ⁢                      i            qs            r                                              [                  Equation          ⁢                                          ⁢          4                ]            
As noted from the Equation 4, the torque of the PMSM (200) is influenced by the d/q axis inductance and the magnet flux linkage of the permanent magnet,
A command generator (110) generates d/q axis current command on synchronous reference frame using relation between command torque and Equation 4. A voltage equation of the synchronous reference frame of the PMSM (200) may be obtained by the following Equations.
                              V          ds          r                =                                            R              s                        ⁢                          i              ds              r                                +                                    L              ds                        ⁢                                          ⅆ                                  i                  ds                  r                                                            ⅆ                t                                              -                                    ω              r                        ⁢                          λ              qs              r                                                          [                  Equation          ⁢                                          ⁢          5                ]                                          V          qs          r                =                                            R              s                        ⁢                          i              qs              r                                +                                    L              qs                        ⁢                                          ⅆ                                  i                  qs                  r                                                            ⅆ                t                                              +                                    ω              r                        ⁢                          λ              ds              r                                                          [                  Equation          ⁢                                          ⁢          6                ]            where, ωr is an electrical angle velocity, Vdsr and Vqsr and d/q axis voltage on the synchronous reference frame, and Rs is a phase resistance on the synchronous reference frame.
The current command generated by the current command generator (110) and feedback current of the coordinate converter (170) are inputted to the current controller (120). The current controller (120) is a proportional and integral regulator, and combines an output voltage in the following manners.
                              V          ds                      r            *                          =                                            (                                                K                  pd                                +                                                      K                    id                                    s                                            )                        ⁢                          (                                                i                                      ds                    ⁢                                                                                  ⁢                    _                    ⁢                                                                                  ⁢                    ref                                    r                                -                                  i                  ds                  r                                            )                                -                                    ω              r                        ⁢                                          λ                ^                            qs              r                                                          [                  Equation          ⁢                                          ⁢          7                ]                                          V          qs                      r            *                          =                                            (                                                K                  pq                                +                                                      K                    iq                                    s                                            )                        ⁢                          (                                                i                                      qs                    ⁢                                                                                  ⁢                    _                    ⁢                                                                                  ⁢                    ref                                    r                                -                                  i                  qs                  r                                            )                                +                                    ω              r                        ⁢                                          λ                ^                            ds              r                                                          [                  Equation          ⁢                                          ⁢          8                ]            where, {circumflex over (λ)}dsr and {circumflex over (λ)}qsr are d/q axis magnetic flux estimated on the synchronous reference frame.
The coordinate converter (130) converts the output voltage on the synchronous reference frame by the current controller (120) to a voltage of stationary reference frame, where the converted voltage is provided as under:Vdss*=Vdsr*cos θ−Vqsr*sin θ  [Equation 9]Vqsr*=Vdsr*sin θ+Vqsr*cos θ  [Equation 10]
The over-modulator (140) regulates the voltage of the coordinate converter (130) and outputs the regulated voltage so that a voltage command can be available within an inscribed circle of voltage restriction condition expressed in a hexagon on the stationary reference frame. The inverter unit (150) combines the following voltages from the output voltage of the over-modulator (140) and applies the voltage to the PMSM (200).
                              V          as                =                  v          ds          s                                    [                  Equation          ⁢                                          ⁢          11                ]                                          V          bs                =                                            -                              1                2                                      ⁢                          V              ds              s                                +                                                    3                            2                        ⁢                          V              qs              s                                                          [                  Equation          ⁢                                          ⁢          12                ]                                          V          cs                =                                            -                              1                2                                      ⁢                          V              ds              s                                -                                                    3                            2                        ⁢                          V              qs              s                                                          [                  Equation          ⁢                                          ⁢          13                ]            
The current sensors (161˜163) measure a phase current between the inverter unit (150) and the PMSM (200), convert the phase current to a current on the synchronous reference frame, and feedback the current to the current controller (120).
                              i          ds          s                =                                            2              ⁢                              i                as                                      -                          i              bs                        -                          i              cs                                3                                    [                  Equation          ⁢                                          ⁢          14                ]                                          i          qs          s                =                                            i              bs                        -                          i              cs                                2                                    [                  Equation          ⁢                                          ⁢          15                ]                                          i          ds          r                =                                            i              ds              s                        ⁢            cos            ⁢                                                  ⁢            θ                    +                                    i              qs              s                        ⁢            sin            ⁢                                                  ⁢            θ                                              [                  Equation          ⁢                                          ⁢          16                ]                                          i          qs          r                =                                            -                              i                ds                s                                      ⁢            sin            ⁢                                                  ⁢            θ                    +                                    i              qs              s                        ⁢            cos            ⁢                                                  ⁢            θ                                              [                  Equation          ⁢                                          ⁢          17                ]            
However, the PMSM (200) is saturated in magnetic flux according to load condition to generate a difference between the torque to be outputted by the inverter (100) and the actually outputted torque, the explanation of which has been described above.
That is, the driving of the PMSM (200) as in FIG. 1 is problematic in that performance decreases in terms of torque control, if inductance of the PMSM (200) or magnetic flux linkage by the permanent magnet is saturated according to load condition, because the d/q axis current command on the synchronous reference frame is calculated by the torque command.